Radio tuning and selectivity control



E 4L B A T. X U H K C y RADIO TUNING AND. SELECTIVITY CONTROL Filed June 21, 1934 INVENTOR Clyde f. /L/Uxale BY G3. QW

I ATTORNEYS lilllllllcallal |||n|||\ Ill' Patented Dec. l0, 1935 PATENT ori-'ics RADIO TUNING AND SELECTIVITY CONTROL Clyde K. Huxtable, Flushing, N. Y., assignor to Hazeltine Corporation, a. corporation of Dela- Application June 21, 1934, Serial No. 731,636

12 Claims.

This invention relates primarily to radio broadcast receiving systems, the tuning and selectivity of which are adjustable by the user for the purpose of receiving a desired station with optimum fidelity consistent with freedom from interference.

In a copending application of Harold A. Wheeler and Nelson P. Case, Serial No. 696,990, filed No'- vember 7, 1933, there is described a radio receiver of the type referred to wherein the tuning and selectivity may be independently and arbitrarily adjusted by means of a unitary control shaft capable of translational and rotational movement. This shaft is axially displaceable tol adjust, at any given frequency of tuning, the selectivity between maximum and minimum limits by variation of the separation between inductlvely coupled tuned tra-nsformer coils. The shaft carries a pinion which at the axial displacement corresponding to maximum selectivity or sharpest tuning, meshes a gear mounted on the shaft of a gang condenser, whereby rotation of the control shaft adjusts the tuning.

In the system of the copending application referred to the control shaft is rotatable at all positions of axial displacement, i. e., irrespective of whether or not the pinion mounted thereon is entrained with the gear of the tuning control. In contradistinction, the present invention provides a mechanical arrangement for maintaining the tuning control continuously engaged for all adjustments of the selectivity control but adds a locking feature to prevent operation of the tuning control except when the selectivity control is adjusted for substantially minimum band width or maximum selectivity.

It is a feature of the present arrangement that the transition from an unlocked to a locked tuning condition takes place smoothly with no additional effect regardless of the adjustment of the tuning control.

The preferred mechanical arrangement consists of a pair of contiguous cylinders of equal diameter, one attached to or frictionally driven by the axially displaceable and rotatable control shaft, the other free to [rotate about the shaft. A pair of soft rubber rollers with axes in a plane perpendicular to the shaft are mounted on fixed supports so as to be continuously in friction contact with one or the` other of the cylinders depending on the axial displacement of the control shaft. The rollers are placed on opposite sides of the shaft to eliminate lateral stress on the shaft. Axial motion is then permitted by the rotation of the rollers about lillgil' gages, during (Cl. Z50-20) lwhich the points of contact move from one cylinder to the other. 'Ihe rubber rollers effectively prevent any rotation of the fixed or frictionally driven cylinder when in contact therewith; but permit the fixed cylinder to be driven by the shaft to effect tuning adjustment when the rubber rollers contact the free or idling cylinder. It

is desirable to knurl the cylindrical surfaces longitudinally or to use pinions for this purpose to decrease the tendency of the rubberrollers to l0 slip.

It is also desirable to provide against forceful stripping of the rubber roller by a careless user in attempting to rotate the control shaft knob in the locked position. This may be done by providing a friction drive between the control knob and shaft or between the shaft and the fixed cylinder, so proportioned. that the friction drive will slip before the cylinder turns against-the rollers.

In the accompanying drawing:

Fig. 1 is a schematic circuit diagram of a superheterodyne radio receiving system the tuning and selectivity of which are independently adjustable by the mechanism of the present invention.

Fig. 2 shows in plan View the mechanical as- 25 sembly of a receiver chassis incorporating thecircuit of Fig. 1 and the mechanical tuning and selectivity control of the present invention.

Fig. 3 is a sectional elevation along 3 3 of Fig. 2. Fig. 4 is a detail .in longitudinal section of the control shaft as terminated in a knob mechanically coupled to the shaft through a frictional drive as explained.

In the circuit of Fig. 1, the antenna-ground system ll-I2 is coupled to a tuned antenna coupling transformer i4 comprising primary coils l5 and I5 and a secondary co'il I1. 'I'here is inductive coupling between coils I6 and I1. There is also inherent capacitive coupling provided between coils'l'l and I5 due to their proximity. The transformer I4 is more fully described in United States Patent 1,907,916, of Harold A. Wheeler, granted May 9, 1933. i

Transformer I l is includedy in a tuned preselector I3 composed of two tunable circuits, the /rst of which comprisessecondary coil l1 and its associated Variable tuning condenser i8, and the second of which comprises a secondary coil I9 and its associated Variable tuning condenser 50 2t. These two tunable preselector circuits are coupled together by a coupling coil 2l which acts as a primary coil with respect to secondary coil i9, and are also coupled by a condenser 22 conbooted between ground and the junction of coils I9 and 2i. The type of double-tuned preselector coupled in the manner described above is described in United States Patent 1,927,672, of Harold A. Wheeler, granted September 19, 1933. It is well known that when the v inductive coupling between two tuned circuits, such as the two tunable circuitsof the preselector, is increased, the admission band width of the coupling system is increased without shifting the center frequency of the band. Such a coupling system is a band-pass selective network, or band selector. When the inductive coupling is increased beyond a certain amount, the characteristic curve of the band-pass selector develops a double peak. The maximum value of coupling which develops only a single peak is known as the optimum value. Reducing the coupling below optimum reduces the 'band width of the single-peak characteristic until a limiting minimum value is reached. Increasing the coupling above optimum increases the frequency separation of the two peaks of the characteristic, and therefore the band width, but it also makes the individual peaks sharper. This typenf bandpass selector is most useful when the inductive coupling is between half and double the optimum value. 'I'he selectivity of band-pass selectors is inversely proportional to the band width. This eiect is utilized by making the coupling coil 2l movable axially with respect to its associated secondary coil I9, as indicated by the double-ended arrow drawn through coil 2l. Consequently, the selectivity, or band-width, of the preselector may be adjusted at will by moving the coupling coil 2I with respect to coil I9. The output of the preselector is impressed upon a radio-frequency amplifier tube 23 of the pentode type. The output of amplifier 23 is impressed on an oscillator-modulator tube 24 through a tunable coupling system comprising a radio-frequency transformer 25. The primary coil 26 of the transformer 25 is resonated by its associated condenser 21 to a frequency somewhat below the tuning range, and the secondary 28 is tunable by its associated variable tuning condenser 29., A xed condenser 30 is connected in the tuned circuit to improve the alignment of this tunable circuit with those of the preselector, as described in the said Patent No. 1,927,672.

The oscillator-modulator tube 24 is of the so-called 2A7 type, similar to that described in the copending application of Harold A. Wheeler, 'Serial No. 654,327, filed Jan. 30, 1933; and the circuit thereof is of a type described in the copending application of Harold A. Wheeler, Serial .N0`. 654,326, filed Jan. 30, 1933. The tube 24 comprises a cathode 3|, an inner grid 32, an inner anode 33, an outer grid 34, a double screen 35 and an outer anode 36 The oscillator portion comprises a circuit connection between the er anode 33 and ground, this circuit including a coil 31 and a coil 38 in series with a radio-frequency by-pass condenser 39 Coil 31 is shunted by an adjustable condenser 40 foraligning the oscillator at lower frequencies, this condenser remaining fixed after it is finally adjusted, and serving to resonate the coil 31 at a frequency below the tuning range-of the oscillator.

'Ihe coils 31 and 38 of this anode circuit are coupled to the inner-grid-circuit, 3|, 32, 33, by an inductive coupling to coil 4I, part of which is connected between the inner gridv32 and-ground.

Coil 4I is shunted by an oscillator tuning con- V denser '42 ,and a fixed condenser 43 in series therewith, the latter serving to the oscillator frequency range. 'I'he cathode circuit is completed to ground by a resistor 44 and a bypass condenser 45. oscillations are produced by the feedback coupling between the inner-anode circuitand inner-grid circuit. voltage across coil 4I is held nearly uniform over the tuning range by proportioning the feedback couplings to coils 31 and 38, the former having more effect at lower frequencies and the latter at higher frequencies.

The radio-frequency signal applied to the outer signal grid 34 from the amplifier 23 is modulated in tube 24 by the oscillations, and the resulting intermediate-frequency product of the modulation appears in the outer-anode circuit 15 of tube 24.

The output of tube 24 is coupled by a doubletuned transformer 46 to an intermediate-frequency amplifier 41 of the pentode type. The primary coil 43 of transformer 46 is tuned by a 20 condenser 49 to the intermediate frequency, and the secondary coil 50 is tuned to the intermediate frequency by a condenser 5I. Condensers '49 and 5I are each adjustable, but when finally tween the coils 43 and 5I, in order to avoid errors 35 due to the double-peak characteristic produced when the coupling exceeds optimum.

The output of amplier tube 41 is coupled to amplifier tube 53 through a double-tuned intermediate-frequency transformer 54. The latter, 40

Awhich is similar in every essential respect to tuned transformer 45, includes primary and secondary coils 55 and 56, respectively, and tuning condensers 51 and 58 therefor, respectively.

The tube 53 is a composite tube of type 2B1 45 comprising a pentode intermediate-frequency amplifier and a diode rectifier. The diode rectier elements are the cathode 59 and the diode anode 60. The cathode 59, the control grid 52, the screen 6I, the suppressor 62 and the anode 50 63 are the electrodes of the vpentode amplifier. The intermediate-frequency signal is amplied in the amplifier-.portion of tube 53, and conducted to a double-tuned intermediate-frequency transformer 64 generally similar to transformers 46 55 and 54. Transformer 64 comprises primary and secondary coils 65 and 66, tuned by condensers 6 1 and 63, respectively. c

The output of transformer 64, across inductance 66, is impresed between the diode anode 60 89 and cathode 59 through `a condenser I3 I. The

I ate-frequency .double-tuned transformers, when the resultant band selection characteristic of the 'I'he oscillation 5 latter is adjusted to develop a double peak. Resistor 76 and condenser 'l1 function as a grid leak and an audio-frequency by-pass condenser, respectively.

The output of tube 1| includes in series, a resistor 78, an audio-frequency coupling condenser 19 and a variable attenuator 80. Attenuator 00 is variably tapped to the input of an audiofrequencyV amplifier indicated di-agrammatically by rectangle 8|, the attenuatpr serving thus as a volume control. The audio system 0| includes any desired conventional apparatus such as a power amplifier terminating in a loudspeaker L.

There is associated with the receiver a system of automatic volume control which functions to maintain the response of the receiver substantially constant over a wide range of received signal intensities. This automatic volume control comprises a tube 83 of type 2B1, which is a combined pentode amplifier and diode rectifier like tube 53. The intermediate-frequency output voltage of the coupling tran-former 54 is impressed on the amplifier control grid 84. The amplied signals appearing in the circuit of anode 85 are coupled by a .double-tuned intermediate frequency transformer 86 to the diode anode 81. The coupling transformer 66 comprises primary coil 86 tuned by condenser 89, and secondary coil 90 tuned by condenser 9|. This transformer. possesses a band-pass characteristic which is much wider than that of transformers 46 and 54. A rectied uni-directional voltage responsive to the intermediate-frequency carrier is developed across resistors 92 and 93 connected in series between the cathode 94 and the secondary coil 90.

The uni-directional voltage across resistors 92 and 93 is impressed on the control grids of tubes 23, 24, 4l, by means of the connections including resistors 95, 96 and 9'|.`

For the purpose of facilitating and obtaining the proper tuning adjustment, which would otherwise be somewhat dilcult owing to the typical action of the automatic volume control arrangement, a visual tuning meter 98, or other visual tuning indicator, is connected in the cathode lead of the first radio-frequency amplifier 23. Since the anode current of the tube ows through the tuning meter, an indication of minimum direct current is that of accurate tuning. The system of automatic volume control and visual indication of tuning described above, is that of United States Patent No. 1,879,863, of Harold A. Wheeler, issued September 27, 1932, and of his application Serial No. 203,879, filed July 7,1927.`

There is also provided a connection 99 from a point between resistors 92 and 93 to the grid circuit of audio amplifier 'll to control or vary the gain thereof. This improvement in automatic volume control is disclosed in the copending application of Harold A. wheeler, seriai No. soa,-

560, led April 6, 1932.

The tubes 23, 24, 41 and 1|, have control grids of the gradual cutoff type. Such a control grid characteristic improves the automatic volume control operation.

There are provided throughout the receiver, resistors and by-pass condensers, as` shown, to improve the general operation. Although batteries are used to designate direct voltage sources throughout the receiver, it s'hould be understood 'that these are only symbols, and may represent, for example, a single source of rectified alterhating-current source with the usual ripple filter,

by-pass condensers and voltage-dividing resistors.

It is noted that the double-ended arrows associated with the transformer primary coils 2|, 48, 55 and 65, denote movable or adjustably coupled coils. It is also noted that condensers having diagonal arrows are uni-controlled variable tuning condensers, while condensers having diagen-al lines without arrow heads are adjustable condensers which remain fixed after the required adjustment has been made.

Referring to Figs. 2 and 3, which illustrate a preferred mechanical arrangement of the receiver of Fig, 1, the apparatus is mounted upon a chassis pan |00 which is of a conventional form having the sides and ends thereof bent downward at a right angle to form a raised horizontal base. Upon the upper side of the chassis is a metal frame |0| which supports the variable tuning condensers I8, 20, 29, and 42 of Fig. 1; These condensers are not shown in .detail in Fig. 2, since they are of a conventional form mounted in line upon a shaft |02 for uni-control operation. The end of the shaft has fastened thereto a gear |03 adapted to be driven by a pinion 04 o which is mounted upon a control shaft |05. A

knob '|06 is fastened to the end of control shaft |05 outside the chassis pan. This knobcontrols different properties of the selective network, as will be described hereinafter;

Situated in line along the center of the chassis pan is a row of shielding cans H9, |20, |2I, |22

and |23, mounted above the pan. Each of these systems is mounted in the shielding can enclosing it, while the movable primary coil is mounted coaxially below it and is adapted to be moved in. an axial direction on a mounting lug and core extending through an opening in the chassis pan.

Fig. 3 shows how this adjustment of each of the t movable primaries is obtained. This figure shows the .position of shaft |05 under the chassis pan and also shows in section the shielding can |22 containing the fixed secondary coil 56 and the movable primary coil 55 of intermediate-frequen- .i

cy coupling transformer 54. The construction and mechanical arrangement of the selective coupling systems, as described herein, have proved successful in practice, but other equivalent mechanical arrangements and specic relative modes of motion of the coils may be employed.

For simplicity of illustration, the only shielding can shown in section in Fig. 3, is can |22, although it will be understood that the remaining cans enclosing movable coils are similarly mounted. In can.|22 the secondary coil 56 is mounted on a core supported from within the top of the can. Primary coil 55 is supported, coaxially with .respect to coil 56, on a core carrier by mounting lug H5. The opposite end of the mounting lug is supported on a rigid cross member H2 along the underside of the chassis pan directly beneath all of the cans |19, |20, |2|, |22 and |23. The cross member ||2 is supported at 'its ends by two crank supports 3 and H3. These crank sup- Can 9 encloses -about :their axes.

ports are mounted on a shaft ||4 along the rear of the chassis pan, parallel to the cross member ||2. The vertical position of cross'.member ||2 is determined by a rigid projecting lug attached at one end to member ||2, and engaging at the other end a notch |29 in a bell crank |08, the latter being mounted o n a shaft |09. To counterbalance the weight due to projecting arm I I I acting on one side of the bell crank, the opposite side of the bell crank is attached to a counterweight ||0.

'I'here is fastened to the inner end of the control shaft |05 a disc |01 which engagesa slot |30 in bell crank |08. 'Ihe shaft |05 is movable by knob |06 in an axial direction which is a degree of freedom termed translation, so that the position of the bell crank and the resulting elevation of coil 55 (and of all other coils movable therewith) is determined by the axial position of the shaft |05. `Movable coils 2|, 46, 55 and 65, are supported on mounting lugs, similar to lug ||5, which are, in turn, mechanically secured to the cross member |2 so that the coils move in unison to like extents by translation of shaft |05. Axial movement of the knob thus simultaneously varies the coupling between coils 2| and I9, 48 and 50, 55 and 56, and 65 and 66, and thereby adjusts the band width of the selector and hence the selectivity of the receiver.

'Ihe control shaft |05 carries a wide faced cylinder or pinion gear |04 which, within the limits of axial displacement of shaft |05, continuously engages a cylinder or gear |03 keyed to shaft |02 supporting the rotor elements of all of the tuning condensers. A second cylinder or pinion |30 of equal diameter to |04 is rotatably supported on shaft |05 in juxtaposition to |04. A pair of soft rubber rollers |3| frictionally engaging cylinders |04 or |30, depending on the axial displacement of shaft |05, are rotatably mounted by means of brackets |32 axed to the chassis |00, on opposite sides of shaft |05 with their axes |33 in a plane perpendicular to shaft |05.

Either pinion |04 or the control knob |06 preferably engages shaft |05 with a frictional drive so proportioned in relation to the frictional contact with which the rubber rollers |3| engage cylinder |04, that the frictional drive will slip before pinion 04 turns against rollers |3|. 'Ihus so long as rollers |3| are in contact with cylinder |04 the tuning control shaft |02 is locked against adjustment by the control knob |06.

Axial motion of shaft |05 to vary the selectivity in the manner explained and without affecting the tuning, is permitted by rotation of rollers |3| The length of cylinder |04 is such in relation to the limits of axial displacement of shaft |05 that rollers |3| will frictionally engage and thus prevent rotation of cylinder |04 for all selectivity adjustments less than substantially the `maximum obtainable with knob |06 pushed in to its limiting position.

As knob V|06 approaches this limiting position the contact points of rollers |3| p'ass from cylinder |04vto the idling cylinder |30. Thereupon rotation of knob |06 will produce corresponding rotation of cylinder |04 through the mentioned frictional drive.V Cylinder |04 will in turn rotate cylinder |03 either through a frictional drive or gear entrainment depending on the surfacingof these cylinders. In this way tuning adjustment is effected by operation of the tuning control shaft |02 keyed to cylinder |03. j,

Fig. 4 illustrates a type offrictional drive that may be employed to couple either cylinder |04 or control knob |06 to shaft |05. The drawing shows the frictional drive as applied to the control knob.

The shaft is provided with a peripheral flange |40 near its end and the knob provided with l bores conforming to the contour of the shaft terminus. The inner bore of the knob houses an end bearing plate |4| for the shaft. Aflixed to an inner edge of knob |06 by means of screws |42 is a ring |43 provided with radially projecting spokes |44 resiliently engaging ange |40 of shaft |05 through the intermediary of frictionally engaging pads |45 of rubber or the like. The tension provided by spokes |44 is such that knob |06 will slip on shaft |05 before cylinder |04 will move 15 against the friction of rollers |3|.

I claim:

Y 1. In a modulated-carrier receiver, a band-pass selector, tuning control means for tuning the re-l ceiver over a range of frequencies, .selectivity 20 control means for independently varying the band width of the selector, and means for mechanically locking the tuning control to prevent its adjustment when the selectivity control is adjusted for substantially greater than minimum band width.

2. In a modulated-carrier receiver, a band-pass selective network, a single knob for controlling different properties of the network, tuning control means for varying the center frequency of the band by rotation of the knob, selectivity control means for independently varying the band width of the network by motion of the knob in the axial direction, and interlocking means for preventing rotation of-the knob when the knob is adjusted for substantially greater than minimum band width.

3. 'I'he arrangement for permittingthe axial displacement of a shaft while preventing its rotation for a portion of said displacement, comprising a rst cylinder rotatable about the shaft 40 as an axis, a second cylinder attached to the shaft, said second cylinder being of equal diameter to said first cylinder and in juxtaposition thereto, and a roller rotatable about a fixed axis `in a plane perpendicular to the shaft and so disposed relative thereto that axial displacement of said shaft automatically effects friction contact between said roller and the surface of said second cylinder for said portion of the displacement to hold said shaft against rotation while permitting free axial movements thereof at all angular positions, and that of said first cylinder for the remainder of the displacement.

4. The combination of an arrangement accord-l ing to claim 3, a knob, anda friction drive between knob and shaft for manual control of the motions of the shaft, said friction drive being pro. portioned to cause the torque produced on the l shaft by rotation of the knob to be greater than that required to rotate the shaft within said mst cylinder and less'than that required to rotate said y second cylinder against-said roller.

5. The arrangement for Vpermitting the axial displacement ofA al cylinder while preventing its rotation for a portion of said displacement, comprising an auxiliary cylinder equal in diameter to the rst said cylinder, both said cylinders mounted in juxtaposition upon a shaft as an axis and rotatable with respect thereto, a roller rotatable about a fixed axis in a plane perpendicular to said shaft, said roller being in friction contact with the surface of said first cylinder for said gportion of the displacement and said auxiliary cylinder for the remainder of the displacement, Y the torsional resistance to rotation vof said firstnamed cylinder about said shaft being greater than that of said auxiliary cylinder about said shaft and less than that of said first-named cylinder with respect to said roller.

6. In a radio receiver having a band-pass selector, a control knob and shaft capable of rotation and axial displacement, a meshed gear and pinion, said gear attached to a tuning device and said pinion attached to said shaft for causing said rotation to adjust the tuning of the receiver, a friction lock for preventing said rotation for a portion of said axial displacement, means for causing said displacement to adjust the band width of said selector, said portion of the displacement corresponding to greater than minimum band width, and the remainder of said displacement corresponding to substantially minimum band width, an auxiliary gear of equal diameter to said pinion and rotatable about said shaft; said friction lock comprising said pinion,

said auxiliary gear, and a roller rotatable about a xed axis in a plane perpendicular to said shaft, said roller being in friction contact with the periphery of said pinion for said portion of the displacement and said auxiliary gear for said remainder of the displacement.

7. In a radio. receiver, a band selector adjust-- able in band width, a rotatable tuning device, a shaft coaxially mounting a pair of contiguous cylinders of equal diameter, one affixed to and the other rotatable about said shaft, said shaft being axially displaceable to vary said band width, said ailixed cylinder being rotatable by said shaft to adjust said tuning device, and a roller rotatable about a fixed axis in a plane perpendicular to said shaft, said roller frictionally engaging said aiiixed cylinder to prevent its rotation for shaft displacements providing in excess of substantially minimum band width, and said roller frictionally engaging said rotatable Vcylinder for shaft displacement providing substantially minimum band width.

8. In a radio receiver, a band selector adjustable in band width, a rotatable tuning device, a shaft coaxially mounting a pair of contiguous cylinders of equal diameter, one affixed to and the other rotatable about said shaft, said shaft being axially displaceable to vary said band width, said affixed cylinder being rotatable by said shaft to adjust said tuning device, a roller rotatable about a fixed axis in a plane perpendicular to said shaft, said roller frictionally engaging said affixed cylinder. to prevent its rotation for shaft displacements providing in excess of substantially minimum band width, said roller frictionally engaging said rotatable cylinder for shaft displacement providing substantially minimum band width, a control knob affixed to said shaft and a frictional drive permitting rotation of said knob 5 without `rotating said aixed cylinder when engaged by said roller.

9. In a signal wave receiver including a bandpass selector, means for tuning the receiver over a range of frequencies, selectivity control means 10 for independently varying the band Width of the selector, uni-control mechanism continuously in operative engagement with both said tuning means and said selectivity control means, and means for preventing adjustment of said tuning 15 means by said mechanism over a predetermined portion of the range of operation of said selectivity control means.

10. In a signal wave receiver including a bandpass selector, means for tuning the receiver over 20 a range of frequencies, selectivity control means for independently varying the band width of the selector, and means for mechanically locking the tuning means, to prevent itsadjustment, over a predetermined portion of the range of operation 25 of said selectivity control means.

11. In a signal wave receiver including a bandpass selector, means for tuning the receiver over a range of frequencies, selectivity control means for independently varying the band width of the 30 selector, a shaft rotatable to operate said tuning means and axially movable to operate said selectivity control means, and means controlled by the axial movement of said shaft for preventing rotation thereof to prevent operation of said tun- .35 ing means over a predetermined portion of the range of operation of said selectivity control means. j

12. 'Ihe arrangement for permitting the axial displacement of a shaft while preventing its roo tation for a portion of said displacement, comprising a cylinder attached to said shaft, and a roller rotatable about a fixed axis in a plane perpendicular to the shaft and so disposed relative thereto that axial displacement of said shaft automatically effects frictional contact between said roller and the 4surface of said cylinder for said portion of the displacement to hold said shaft against rotation while permitting free axial movements thereof at .all angular positions, and auto- 50 matically effects disengagement between said roller and said surface for the remainder of said displacement.

CLYDE K. HUXTABLE. 

